Former officers who served under the South African apartheid regime have claimed they have proof implicating former president PW Botha's inner circle in the 1986 assassination of Swedish Prime Minister Olof Palme, the Dagens Nyheter daily reported on Tuesday.

Palme was gunned down by an unidentified assailant as he walked home from a Stockholm cinema on February 28, 1986.

According to "an original military document" dated November 20, 1985, a copy of which was seen by Dagens Nyheter, Palme's killer was a South African secret agent whose orders came directly from Botha's chief security advisor, who was not named.

The document was a letter sent to the chief operating officer of the apartheid regime's secret police, Craig Williamson, whose name has already surfaced in the murder investigation.

According to the letter, which refers to the operation by the codename "Slingshot", Palme was to be murdered between February 21 and 23, 1986, during an anti-apartheid conference, which was attended by African National Congress (ANC) leader Oliver Tambo.

Palme was actually shot one week later.

Dagens Nyheter first claimed on Monday that South African secret services had a hand in Palme's assassination.

However, Swedish police said they were skeptical about the paper's report that former military intelligence and security officials had singled out a South African agent as Palme's murderer.

The claims are based on research by former high-ranking South African soldiers, who acquired their country's military archives and interviewed agents. Their work has been financed by Swedish businessman Kent Ajlandet and a former Swedish police chief, Tommy Lindstroem.

A former South African navy officer, Ponnie van Vuuren, told Dagens Nyheter that he had no doubt about the identity of the killer.

"We have all the evidence, including the documents revealing who gave the orders, the motive, and the perpetrator," he said.

"The murderer has been on the run for 17 years ... He has no income, and no job. He is holding a fake passport," he said.

A possible South African connection in the murder has been one of the police's main line of investigation, along with a Kurdish link and the theory that the gunman was acting on his own.

Palme was a vociferous opponent of South Africa's apartheid policies - Sapa-AFP.